1. Field of the Invention
This invention relates to a prosthesis which can be used without bone cement, a preformed mantle for use with such a prosthesis and a method of attaching such a prosthesis to the bone.
2. Description of the Prior Art
U.S. Pat. No. 3,918,100 proposes the use of sputtering to apply a layer of coating material directly onto a metal prosthesis. The process requires complicated and expensive equipment and it is not clear whether it was ever used successfully. The intention appeared to be to coat the prosthesis and then place it in the bone, relying on the coating of bone particles to promote bone growth and attachment to the living bone.
U.S. Pat. No. 4,168,326 relates to a prosthesis covered with an enamel or enamel-like coating to which bioactive material was applied. Once again, the intention was to use the prosthesis without bone cement. This construction also called for expensive and complicated procedures.
U.S. Pat. No. 4,650,489 proposed a prosthesis which was provided with a metallic external sheath. The prosthesis member is attached to the sheath by elastomeric material so that there is a shock absorbing effect. In this construction the sheath is said to have an outer irregular surface to provide for regrowth of bone. It is stated that in the growing process the bone integrates with the sheath resulting in a cancellous or spongy bone. Once again, no cement was used but the whole intention of this device is to provide shock absorbing. The use of roughened surfaces on metallic components in prostheses is of course well known in itself.
U.S. Pat. No. 4,795,472 relates to a hip stem having a polymer coating fixedly attached to a textured surface of the stem.
It is well-known, for example as shown In European Publication No. EP 0 457 464 A1 (U.S. Ser. No. 701,556), the teachings of which are incorporated herein by reference, to provide a prosthesis with a sheath in the form of a preformed cement layer which can be fitted to the implant as a separate component. The purpose of the layer provided by the sheath is to guarantee that there is a minimal cement thickness separating the implant from the bone; and to produce a better implant cement interface for in-service taper re-engagement. In this arrangement the device is assembled to the preformed cement sheath and the surgeon implants the assembly using freshly mixed bone cement.
It is important that there is an effective engagement at the bone cement/bone interface in total joint replacement. If the engagement becomes loose, internal damage occurs to the bone which rapidly accelerates the loosening effect to such an extent that the joint becomes inoperable.
It has been found by experiment that a prosthesis can be implanted with the inside of the opening in the bone filled with bone chips rather than bone cement. A very thin layer of bone cement is provided which separates the implant from the compacted internal bone graft. It has been found that the results are excellent and there is immediate adhesion between the thin layer of bone cement and the adjacent and contacting bone chips.
The present invention is intended to take advantage of the technique referred to above so as to provide a prosthesis and a method of attaching it which eliminates the time consuming and messy operation of handling fresh bone cement during an operation.